305 head on a 350 SBC? Why?

[hauserdaddy]

I have a 78 280Z that came from the PO with this setup.

 

1974 SBC 350,

Bottom end is rebuilt to stock specs with less than 2000 miles on her.

Top end is a 305 head(500 miles).

477 lift cam,

performer intake,

new holley 650 carb,

Billetproof distributor,

TH350 tranny, Quarter stick shifter,

New shorty headers, Gear drive timing.

 

Car was Dyno'd at 297 hp and 305 foot pounds of torque to the rear wheels.

 

Why go with a 305 head? I know that they increase compression and should give more low end power but unless they're ported and opened up a bit dont they constrict air flow on a 350? I am not looking to increase HP, I just want to ensure that this engine setup is fine for a Z.

 

Thanks!

[grumpyvette]

your correct ,most 305 heads use small valves and small ports, that will restrict a 350 noticably in the upper rpm ranges

 

this may help

 

http://www.ws6transam.org/ported.html

 

http://www.sa-motorsports.com/diyport.shtm

 

 

as will swapping to a better intake manifold ,but theres nothing you can do to a set of standard 305 chevy cast heads that will allow them to make power like a decent set of the better designed aftermarket heads, the ports and valves in the stock heads jwith thire 155cc-167cc ports and 1.94"-/1.5" valves just can,t support the flow levels a 2.02"/1.6" valve config and a 175cc-200cc port will.

if your like most of us Im sure MONEYS a major problem, but the correct combo of heads, cam , compression ratio,and intake can make a huge differance in the power curve, Id start saving for a set of good heads, theres no real rush, but once you install them youll be amazed at the change in the engines performance

[hauserdaddy]

Thanks Grumpy. Unfortunately, I just dont know how much was done to the head. Obviously it has to have had some work done to it in order for the car to hit 300 HP at the wheels (porting and dished pistons maybe?). I guess I would be increasing performance by going to an aftermarket head but really, how much more am I going to crank out of stock spec 350?

[280zwitha383]

Car was Dyno'd at 297 hp and 305 foot pounds of torque to the rear wheels.......I just want to ensure that this engine setup is fine for a Z.

 

Thanks!

 

If it's already in the car and you have driven it why do you ask? Seems you should be able to have plenty of fun with that setup... for a while

[dr_hunt]

Thanks Grumpy. Unfortunately, I just dont know how much was done to the head. Obviously it has to have had some work done to it in order for the car to hit 300 HP at the wheels (porting and dished pistons maybe?). I guess I would be increasing performance by going to an aftermarket head but really, how much more am I going to crank out of stock spec 350?

 

 

Some decent heads will boost the low end and raise the peak HP, the biggest gains should be in TQ. You will see more area under the curve, which means alot. Peak dyno numbers don't mean squat. 1100rwhp 'stangs here in alb are only running 10.80's in the 1/4, so you can see that peak #'s don't mean much. As for how much, probably 50hp with aftermarket heads. But as grumpy says, it's the total package that counts, so if you were going to do a bottom end, then I'd add better heads. Till then run what you have. I'd bet that car kicks some booty on the street??!!

 

IMO the 305 heads are junk, prone to cracking, restrictive flow, small valves, complete waste of time and energy given what else is available today. Even some 882 castings would be better IMO.

[Sven]

There was a 305HO in 80's vettes. Tiny chambers... more compression, bigger ports. I'm sure that head could be found pretty cheap. I had a friend who ported a set of those, and ran it on a 350 in a 68 Chevelle. The car ran in the 12.4-12.1 1/4 mi range. The Chev was a fat pig too, not stripped at all.

 

But, unless you could pick these up for next to nothing, it probably isn't worth it. There are so many aftermarket alum heads out there now that can make serious power. The market is flooded and some are dirt cheap.

 

As everyone's said, enjoy it now! Come winter build a big romp-em, stomp-em motor. It will give you something to compare to next year.

 

BTW, 305's suck. My buddy Kevin built one (moderately), and could still only manage 13 sec... with nitrous.

[hauserdaddy]

I dont plan on changing a thing because the car seems to run fine. I just wanted opinions on the 305 head because you guys have quite a bit more knowledge than I on this stuff. This head may very well be a High output head. I better start pulling part/casting numbers if I really want to get more info

[ecp48]

With those heads you probably have the Summit reversed D shape Popup pistons. The recess in the piston matches the shape of the combustion area. Porvides excellent squish area and allows a higher compression without detonation. Ports would definitely need to be reworked for horsepower, but they should provide excellent low end torque. The 305/corvette aluminum heads with these pistons was part of an engine package that Summit used to sell.

[LS1 240Z]

305 heads bump up the compression and make it have lotso torque

 

its a cheap way to bump up compression, and making close to 300 hp at the wheels is most impressive.. shows you that the heads arent that restrictive. but yeah, you should get some like L98 heads or some aftermarket heads and you would see great gains

[Pyro]

300 hp to the wheels is about 360 at the crank.

 

360hp only requires 180cfm at max lift, in your case, 0.477 inches. That isn't a lot of flow. 220+ cfm is what most good aftermarket heads flow at that lift.

 

Install some better heads and the power will go up. Those heads are most likely maxed out.

 

Sometimes people use 305 heads just because they have a set laying around.